Hybrid vehicles include both a gasoline engine and an electric motor. One big benefit of the hybrid vehicles is that the gasoline engine and electric motor are each used for what they do best. Particularly, the gas engine allows for long range on a high-density power source (gasoline), while the electric motor allows efficient capturing and reusing of “excess” energy. Another benefit is that hybrid vehicles offer low emissions and high fuel economy.
Generally, in consideration of complexity of installation process and costs for research and development, soft type hybrid power trains, which have typical a structure of conventional automatic transmissions except for an additional motor to supplement the power of the engine, are advantageous compared to hard type hybrid power trains.
However, in such conventional soft type hybrid power trains, the engine and the motor are operated always in conjunction with each other. As a result, hybrid vehicles equipped with such hybrid power trains are difficult to be started purely in an electric vehicle mode in which only a motor is operated while an engine is stopped.
There is thus a need for an improved power train structure that can operate a hybrid vehicle solely in an electric mode at an initial startup stage and in a low speed range, thereby offering lower emission and higher fuel economy.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.